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A lifetime of feeling hungry- second US primate experiment contradicts the first

The results of a second lifetime experiment in non-human primates in the US were widely reported in the scientific media last month. Researchers at the National Institute of Aging (NIA) in the USA kept rhesus macaques (Macaca mulatta) on a restricted diet for their entire lives, feeding them 30% fewer calories than normal. In contrast to an almost identical experiment conducted at Wisconsin National Primate Research Center (WNPC) also in the USA, they found that those on the restricted diet did not live longer.

The rise of the ‘western diet’ over the last century has prompted researchers to conduct hundreds of experiments in a bid to discover if our eating habits have an effect on our lifespan. It has been shown in mice and rats that reducing overall food intake improves survival. In an attempt to replicate these results in longer living species, these two independent research centres initiated separate experiments in the 1980’s using rhesus monkeys to prove that calorie restriction leads to longer life. 

After 25 years, the results of both experiments have finally been published. Much to the disappointment of scientists, the results are contradictory, with the NIA study failing to show that living on a restricted diet makes you live longer. The apparent reason for this is that the monkeys at the NIA were fed a much healthier diet compared to the monkeys at the WNPRC who were free to eat as much of their high sugar diet as they pleased, leading to the development of diabetes in more than 40% of the animals. Thus, monkeys in the ‘restricted group’ of the WNPRC study only seemed to live longer by comparison simply because they ate less of the unhealthy diet.

Many of the animals in these studies actually died from non-age-related causes such as stomach bloat, injury or during surgery demonstrating the suffering they experienced by being forced to spend their entire existence (over 20 years) in cages. 50% of the primates in the WNPC study are still alive. 

According to his studies on human centenarians, a gerontologist at Albert Einstein College of Medicine in New York, Dr Nir Barziali, believes that genetics is much more important than diet and lifestyle in determining how long a person will live. It seems, therefore, that these studies in primates were not only cruel and badly designed, but fairly pointless.